The invention relates to a powershiftable multistage transmission operating between an input shaft, which can be connected to a first shaft of the transmission, and an output shaft as a second shaft of the transmission, comprising two shaft-lines which are arranged in parallel in one transmission housing, three transfer gears, three planetary gears and several shifting elements, said first shaft-line having the first shaft as well as a third shaft, a fourth shaft and a fifth shaft and said second shaft-line having the second shaft as well as a sixth shaft, a seventh shaft and an eighth shaft, whereat the third shaft and the sixth shaft are connected by a first transfer gear and the fourth shaft and the seventh shaft are connected by a second transfer gear and the fifth shaft and the eighth shaft are connected by a third transfer gear and whereat a first planetary gear is arranged on the first shaft-line and has a first sun gear a first ring gear and a first planet-carrier, whereat a second planetary gear is arranged on the first shaft-line or on the second shaft-line and has a second sun gear a second ring gear and a second planet-carrier, whereat a third planetary gear is arranged on the second shaft-line and has a third sun gear a third ring gear and a third planet-carrier.
The Japanese paper JP 2000-304110 A describes such a powershiftable multistage transmission. In the various concepts of the transmission according to this state of the art the second planetary gear is arranged on the second shaft-line. For the shifting of up to six forward speeds and one reverse speed this transmission has five shifting elements, three clutches and two brakes. With these shifting elements certain gear elements can be linked together or to the transmission housing to get a definite kinematic situation and power-paths for a torque transmission with a certain ratio. A disadvantage of this transmission is that with this number of shifting elements only six forward speeds can be switched. But for further reduced fuel consumption and for even better driving dynamics vehicles need more and tighter stepped gears.
US patent application publication no. US 2006/0142111 A1 (=DE 10 2005 018 804) also describes powershiftable multistage transmissions which have two shaft-lines which are connected by three transfer gears. Most of the transmissions according to this state of the art have three planetary gears each with a sun gear a ring gear and a planet-carrier. But mostly two of the planetary gears are arranged on the first shaft-line. Also in these transmission concepts only six forward gears can be realized with only five shifting elements. For seven or eight forward speeds at least six shifting elements are necessary.
PCT international application no. WO 2006/074707 (=DE 10 2005 002 337) describes powershiftable multistage transmissions in which only five shifting elements are enough for eight well stepped forward gears and one reverse gear. It is a special feature and an advantage of these concepts, that in each gear always three of the five shifting elements have to be closed. That means that only two of five shifting elements are sliding and creating some sliding losses in each gear. In all variants according to this paper the gear sets of the transmission are four planetary gear sets, which are arranged coaxially on only one shaft-line. Each of the planetary gear sets has only three elements (sun, carrier, ring). This coaxial arrangement of four planetary gears is the reason why such a transmission becomes long and not very well suitable for front-cross-applications. Furthermore the coaxial arrangement of the planetary gear sets on only one shaft-line leads to the disadvantage, that at some points of the transmission up to five shafts are running within each other. That makes the arrangement of bearings complex. Furthermore in some versions of the transmission relatively long hollow shafts are necessary to connect elements over long distances. Furthermore it is a disadvantage, that in no transmission, described in this paper, all clutches can be fed with oil from the housing only through one oil transmitter between parts with relative speed. The oil supply of at least one clutch has to be done through two of such oil-transmitters, which means through an additional shaft.
In the above mentioned patent application there is a favorable stepping of the ratios of the eight forward speeds mentioned with φges=7.05 and a direct speed in the sixth gear. The analysis of this transmission shows, that the stationary ratios of the planetary gear sets to achieve this ratio stepping can be designed properly. But to achieve much different ratio steppings the stationary ratios have to become too big or too small, so that the transmission design will become difficult.
To reduce the fuel consumption more and more electric motors and electric accumulators will be integrated into future drivelines. By means of such devices an energy management allows to let the internal combustion engine to operate more efficient or to switch off the internal combustion engine whenever it is not necessary to let it run. By means of boosting, purely electrical driving and regenerative braking it is possible to get further potentials to save energy. The best position to link an electric motor to a driveline is somewhere in the transmission, because by such an optimal linkage the ratios of the transmission can reduce the loads on the electric system in most of the operating points. In most cases then a small electric motor is sufficient to get big benefits.
In this context it is claimed in WO 2006/074707 that an electric motor can be linked to each shaft of the transmission. But there are only those shafts suitable for a link to an electric motor which can be also linked directly to the transmission housing. But in the transmission structures, described in this state of the art, an electric motor can not be linked to the most suitable shaft.
All powershiftable multistage transmission concepts according to the state of the art with two shaft-lines, three transfer gears and three planetary gears can only shift six forward speeds and one reverse speed with only five shifting elements. To get up to eight forward speeds with only five shifting elements only concepts with four planetary gears which are coaxially arranged on one shaft-line are known.